Organic EL display device

ABSTRACT

A the organic EL display 1 includes: a first substrate 10; an organic EL element 4 provided above the first substrate 10; and a multilayer sealing film 2 provided above the first substrate 10 to cover the organic EL element 4, and including a barrier layer and a buffer layer lower in hardness than the barrier layer. The organic EL element covered with the multi layer sealing film includes a protrusion, and a relationship (d/h)&lt;2 holds where h is a height of the protrusion directly below the buffer layer and d is a thickness of the buffer layer.

TECHNICAL FIELD

The present application is a divisional application of U.S. patentapplication Ser. No. 15/532,777, now U.S. Pat. No. 10,069,110, filed onJun. 2, 2017, which is the U.S. national phase of InternationalApplication No. PCT/JP2015/005951 filed Nov. 30, 2015, which designateddie U.S. and claims priority to Japanese Patent Application No.2014-246977 filed in Japan on Dec. 5, 2014. The entire disclosure ofsuch parent application, is incorporated herein by reference.

A technique disclosed to the DESCRIPTION relates to an organicelectroluminescence (EL) display device including an organic EL element.

BACKGROUND ART

In recent years, liquid crystal displays are of used as flat paneldisplays in various fields. However, the following problems stillremain. Contrast and tinge greatly vary depending on viewing angles. Aneed for a light source such as a backlight hinders lower powerconsumption. Reduction in the thickness and weight of a liquid crystaldevice is limited. Moreover, liquid crystal devices still have problemsin flexibility.

To address the problems, self-luminous organic EL displays using organicEL elements are expected in place of liquid crystal displays. In anorganic EL element, a current flows through organic EL layers sandwichedbetween an anode and a cathode so that organic molecules forming theorganic EL layers emit light. Being self ominous, organic EL displaysusing such an organic EL element are thin, light, and low in powerconsumption. In addition, organic EL displays provide a wide viewingangle, and thus draw great attention as a candidate for flat paneldisplays in the next generation. Moreover, such organic EL displays canbe superior to liquid crystal displays in terms of flexibility. Takingadvantage of their thinness and wide viewing angle, Organic EL displaysare being put into practical use as main displays for portable audiodevices and cellular phones.

Patent Document 1 discloses a display element including: an effectivepart having display elements; and a sealing body arranged so as to coverat least the effective part of a main surface of a substrate.

The sealing body includes a buffer layer and a barrier layer to keep anorganic EL element from moisture.

CITATION LIST Patent Document

PATENT DOCUMENT 1: Japanese Unexamined Patent Publication No.2006-004650

SUMMARY OF THE INVENTION Technical Problem

The buffer layer included in the sealing body is low in hardness. Whenshear stress is imposed on the buffer layer, the imposed shear stresscan create a continuous line of fracture in the buffer layer, causingdelamination of a film.

The present disclosure is intended to provide an organic EL displaydevice in which a sealing film is less vulnerable to delamination.

Solution to the Problem

An organic EL display device disclosed in DESCRIPTION includes: a firstsubstrate; an organic EL element provided above the first substrate; anda multilayer sealing film provided above the first substrate to coverthe organic EL element, and including a barrier layer and a buffer layerlower in hardness than the barrier layer. The organic EL element coveredwith multilayer sealing film includes a protrusion, and a relationship(d/h)<2 holds where h is a height of the protrusion directly below thebuffer layer and d is a thickness of the buffer layer.

Advantages of the Invention

In the organic EL display device according to the present disclosure,multilayer sealing film is less vulnerable to delamination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating an organic EL displaydevice according to a first embodiment of the present disclosure.

FIG. 2 is a cross-sectional view illustrating a structure of amultilayer sealing film in the organic EL display device according tothe first embodiment.

FIG. 3 is a cross-sectional view illustrating a line of fracture createdin an organic EL display device according to a reference.

FIG. 4 is a cross-sectional view illustrating a line of fracture createdin an organic EL display device according to the first embodiment.

FIG. 5 is a cross-sectional view illustrating a method of manufacturingthe organic EL display device according to the first embodiment.

FIG. 6 is a cross-sectional view illustrating the method ofmanufacturing the organic EL display device according to the firstembodiment.

FIG. 7 is a cross-sectional view illustrating the method ofmanufacturing the organic EL display device according to the firstembodiment.

FIG. 8 is a cross-sectional view illustrating the method ofmanufacturing the organic EL display device according to the firstembodiment.

FIG. 9 is a cross-sectional view illustrating a structure of amultilayer sealing film in an organic EL display device according to asecond embodiment.

FIG. 10 is a cross-sectional view illustrating a structure of amultilayer sealing film in the organic EL display device according to amodification of the second embodiment.

FIG. 11 is a cross-sectional view illustrating an organic EL displaydevice according to a third embodiment.

FIG. 12 is an enlarged cross-sectional view illustrating the organic ELdisplay device according to the third embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will now be described in detailwith reference to the drawings. The present disclosure is not limited tothe following embodiments.

(First Embodiment)

FIG. 1 is a cross-sectional view illustrating a organic EL displaydevice 1 according to a first embodiment of the present disclosure. FIG.2 is an enlarged cross-sectional view illustrating a structure of amultilayer sealing film 2 in the organic EL display device 1 accordingto the first embodiment.

As shown in FIG. 1, the organic EL display device 1 includes: an elementsubstrate 10 acting as a first substrate; an organic EL element 4provided above the element substrate 10; and the multilayer sealing film2 provided above the element substrate 10 to cover each of organic ELelements 4. The element substrate 10 contains such insulating materialsas glass and plastic.

The multilayer sealing film 2 includes at least one barrier layer, andat least one buffer layer which is lower in hardness than the barrierlayer. In an example illustrated in FIG. 2, the multilayer sealing film2 includes a barrier layer 31A, a barrier layer 32B, and a buffer layer33 sandwiched between the barrier layer 31A and the barrier layer 31B.

The barrier layer 31A and the barrier layer 31B function to keep theorganic EL element 4 from moisture and oxygen. The buffer layer 33functions to reduce and distribute stress when a barrier layer is formedabove the buffer layer 33 so as to reduce the risk of film delamination.

The buffer layer 33 contains such a material as polysiloxane, siliconoxycarbide, acrylate, polyurea, parylene, polyimide, or polyamide. Thebarrier layer 31A and the barrier layer 31B contain silicon nitride,silicon oxide, silicon oxynitride, or Al₂O₃.

A thickness of the multilayer sealing film 2 may beneficially be, butnot limited in particular to, within a range between 1 μm and 100 μm inview of sufficiently enhancing durability of the organic EL element 4. Athickness of the barrier layer 31A and the barrier layer 31B is within arange between, for example, 0.1 μm and 5 μm. A thickness of the bufferlayer 33 is within a range between, for example, 0.3 μm and 100 μm, andmore beneficially, between 0.3 μm and 5 μm.

The example illustrated in FIG. 2 shows that a top face of the barrierlayer 31B is flat; however, the top face of the barrier layer 31B mayhave a recess and a protrusion in conformity with a recess and aprotrusion of an underlayer below the barrier layer 31B.

The organic EL elements 4 are arranged above the element substrate 10 ina matrix. The element substrate 10 has a display region (a region exceptan end) 15 in which a pixel region 15R emitting red light, a pixelregion 15G emitting green light, and a pixel region 15B emitting bluelight are arranged in accordance with a predetermined pattern.

The organic EL elements 4 include: first electrodes 13 (anodes) arrangedabove the element substrate 10 in a predetermined array (e.g., in amatrix); an organic EL layer 17 formed above the first electrodes 13; asecond electrode 14 formed above the organic EL layer 17; and edgecovers 18 provided to cover peripheral edges of the first electrodes 13and regions in which the first electrodes 13 are not provided. Providedbetween the pixel regions 15R, 15G, and 15B, the edge covers 18 functionas partitions to separate the pixel regions 15R, 15G, and 15B from oneanother.

In the organic EL element 4, a top fare above an edge cover 18 ispositioned higher than other top faces. In other words, the edge cover16 forms a protrusion of the organic EL element 4.

Moreover, as shown in FIG. 1, the organic EL display device 1 includesTFTs 11 and interlayer insulating films 21. Each of TFTs 11 is formedabove the element substrate 10, and electrically connected to acorresponding one of the first electrodes 13. The interlayer insulatingfilms 21 are formed above the element substrate 10 to cover the TFTs 11.The first electrodes 13 are connected to the corresponding TFTs 11 inportions provided in the contact holes 23.

The first electrodes 13 function to inject holes into the organic ELlayer 17. The first electrodes 13 beneficially contain a material with ahigh work function. This is because a material with a high work functionallows the first electrodes 13 to inject holes to the organic EL layer17 with higher efficiency. Furthermore, as shown in FIG. 1, the firstelectrodes 13 are formed above the interlayer insulating films 21.

Exemplary materials for the first electrodes 13 may include metalmaterials such as silver (Ag), aluminum (Al), vanadium (V), cobalt (Co),nickel (Ni), tungsten (W), gold (Au), calcium (Ca), titanium (Ti),yttrium (Y), sodium (Na), ruthenium (Ru), manganese (Mn), indium (In),magnesium (Mg), lithium (Li), ytterbium (Yb), and lithium fluoride(LiF). Moreover, the first electrodes 13 may also be an alloy ofmagnesium (Mg)/copper (Cu), magnesium (Mg)/silver (Ag), sodium(Na)/potassium (K), astatine (At)/astatine dioxide (AtO₂), (Li)/aluminum(Al), lithium (Li)/calcium (CO)/aluminum (Al), or lithium fluoride(LiF)/calcium (Ca)/aluminum (Al). Furthermore, the first electrodes 13may be such a conductive oxide as tin oxide (SnO), zinc oxide (ZnO), orindium tin oxide (ITO), and indium zinc oxide (IZO).

Moreover, the first electrodes 13 may be multilayers containing theabove materials. Materials with a high work function may include, forexample, indium tin oxide (ITO) and indium zinc oxide (IZO).

Formed above the element substrate 10, the interlayer insulating films21 function to planarize surfaces of the TFTs 11. This interlayerinsulating films 21 may planarize the first electrodes 13 and theorganic EL layer 17 to be formed above the interlayer insulating films21. That is, the planarization using the interlayer insulating films 21reduces the risk that steps, protrusions, and recesses of theunderlayers in the organic EL display device 1 influence the shape ofthe surface of the first electrodes 13, causing light emission by theorganic EL layer 17 to be non-uniform. The interlayer insulating films21 contain a highly transparent, low-cost organic resin material such asacrylic resin.

Each organic EL layer 17 is formed on a surface of a corresponding oneof the first electrodes 13 arranged in a matrix. This organic EL layer17 includes a hole injection layer (not shown), a hole transport layer,a light-emitting layer, an electron transport layer, and an electroninjection layer. The hole transport layer is formed on a surface of thehole injection layer. The light-emitting layer is formed on a surface ofthe hole transport layer, and emits any one of red light, green light,and blue light. The electron transport layer is formed on a surface ofthe light-emitting layer. The electron injection layer is formed on asurface of the electron transport layer.

The hole injection layer, the hole transport layer, the light-emittinglayer, the electron transport layer, and the electron injection layerare sequentially stacked to constitute the organic EL layer 17. Theorganic EL layer 17 may be smaller in area than the underlying firstelectrodes 13 or larger in area than the underlying first electrodes 13to cover the first electrodes 13.

The hole injection layer is also called an anode buffer layer, whichapproximates the energy levels between the work function of the firstelectrodes 13 and a highest occupied molecular orbital (HOMO) of theorganic EL layer 17 to increase the efficiency in the hole injection.

Exemplary materials for the hole injection layer may include triazolederivatives, oxadiazole derivatives, imidazole derivatives,polyarylalkane derivatives, pyrazoline derivatives, phenylenediaminederivatives, oxazole derivatives, styrylanthracene derivatives,fluorenone derivatives, hydrazone derivatives, and stilbene derivatives.

The hole transport layer functions to improve efficiency in transportingthe holes from the first electrodes 13 to the organic EL layer 17. Anexemplary material for the hole transport layer may include porphyrinderivatives, aromatic tertiary amine compounds, styryl aminederivatives, polyvinylcarbazole, poly-p-phenylene vinylene, polysilane,triazole derivatives, oxadiazole derivatives, imidazole derivatives,polyarylalkane derivatives, pyrazoline derivatives, pyrazolonederivatives, phenylenediamine derivatives, arylamine derivatives,amine-substituted chalcone derivatives, oxazole derivatives,styrylanthracene derivatives, fluorenone derivatives, hydrazonederivatives, stilbene derivatives, hydrogenated amorphous silicon,hydrogenated amorphous silicon carbide, zinc sulfide, or zinc selenide.

The light-emitting layer is a region in which the holes and theelectrons are injected thereinto from the first electrodes 13 and secondelectrode 14 and recombine with each other when a voltage is appliedfrom the first electrodes 13 and the second electrode 14. Thislight-emitting layer contains a material with high luminous efficiency.The material may be metal oxinoid compounds [8-hydroxyquinoline metalcomplexes], naphthalene derivatives, anthracene derivatives,diphenylethylene derivatives, vinylacetone derivatives, triphenylaminederivatives, butadiene derivatives, coumarin derivatives, benzoxazolederivatives, oxadiazole derivatives, oxazole derivatives, benzimidazolederivatives, thiadiazole derivatives, benzothiazole derivatives, styrylderivatives, styrylamine derivatives, bisstyrylbenzene derivatives,trisstyrylbenzene derivatives, perylene derivatives, perinonederivatives, aminopyrene derivatives, pyridine derivatives, rodaminederivatives, acridine derivatives, phenoxazone, quinacridonederivatives, rubrene, poly-P-phenylene vinylene, or polysilane.

The electron transport layer functions to efficiently transport theelectrons to the light-emitting layer. Exemprary materials for theelectron transport layer may include, as organic compounds, oxadiazolederivatives, triazole derivatives, benzoquinone derivatives,naphthoquinone derivatives, anthraquinone derivatives,tetraeyanoanthraquinodimethan derivatives, diphenoquinone derivatives,fluorenone derivatives, silole derivatives, and metal oxinoid compounds.

The electron injection layer approximates the energy levels between thesecond electrode 14 and the organic EL layer 17 to increase theefficiency in injecting electrons from the second electrode 14 into theorganic EL layer 17, thereby reducing the drive voltage of the organicEL element 4. The electron injection layer may also be called a cathodebuffer layer. Materials for the electron injection layer may include,for example, Al₂O₃, SrO, and such inorganic alkaline compounds aslithium fluoride (LiF), magnesium fluoride magnesium fluoride (MgF₂),calcium fluoride (CaF₂), strontium fluoride (SrF₂), and barium fluoride(BaF₂).

The second electrode 14 functions to inject electrons into the organicEL layer 17. The second electrode 14 may beneficially contain a materialwith a low work function. This is because a material with a low workfunction allows the second electrode 14 to inject electrons into theorganic EL layer 17 with higher efficiency. As shown in FIG. 1 thesecond electrode 14 is formed above the organic EL layer 17.

Materials for the second electrode 14 may include, for example, silver(Ag), aluminum (Al), vanadium (V), cobalt (Co), nickel (Ni), tungsten(W), gold (Au), calcium (Ca), titanium (Ti), yttrium (Y), sodium (Na),ruthenium (Ru), manganese (Mn), indium (In), magnesium (Mg), lithium(Li), ytterbium (Yb), and lithium fluoride (LiF). The second electrode14 may also be an alloy of magnesium (Mg)/copper (Cu), magnesium(MG)/silver (Ag), sodium (Na)/potassium (K), astatine (At)/astatinedioxide (AtO₂), lithium (Li)/aluminum (Al), lithium (Li)/calcium(Ca)/aluminum (Al), and lithium fluoride (LiF)/calcium (Ca)/aluminum(Al). The second electrode 14 may also contain a conductive oxide suchas on oxide (SnO), zinc oxide (ZnO), or indium tin oxide (ITO) andindium zinc oxide (IZO). The second electrode 14 may be a multilayercontaining the above materials.

A material with a low work function may be, for example, magnesium (Mg),lithium (Li), lithium fluoride (LiF), magnesium (Mg)/copper (Cu),magnesium(Mg)/silver (Ag), sodium (Na)/potassium (K), lithium(Li)/aluminum (Al), lithium (Li)/calcium (Ca)/aluminum (Al), or fluoride(LiF)/calcium (Ca)/aluminum (Al).

The edge covers 18 function to reduce short-circuit between the firstelectrodes 13 and the second electrode 14. Thus, the edge covers 18beneficially cover entire peripheral edges of the first electrodes 13.

The edge covers 18 may contain such materials as a photosensitive resinorganic film including polyimide resin, acrylic resin, polysiloxaneresin, and novolak resin, or an inorganic film including silicon dioxide(SiO₂).

As shown in FIG. 2, the following relationship holds in the organic ELdisplay device 1 of this embodiment: (d/h)<2 where h is a height of aprotrusion directly below the multilayer sealing film 2 and d is athickness of the buffer layer 33. Here, the thickness of the bufferlayer 33 means a thickness, of the buffer layer 33, in a region betweenprotrusions. Moreover, the height h of the protrusion directly below thebutler layer 33 is almost equal to a height of a protrusion of theorganic EL element 4. More accurately, the height h of the protrusiondirectly below the buffer layer 33 is equal to a difference in levelbetween (i) a top face of a portion, of the barrier layer 31A, formingthe protrusion and (ii) another top face (a recess) of a portion, of thebarrier layer 31A, formed between protrusions including the protrusion.

The height h of the protrusion ranges approximately between 0.5 μm and 3μm, for example. Here, the height h is 1.6 μm. The thickness d of thebuffer layer 33 ranges approximately between 0.3 μm and 100 μm, asdescribed above, and more beneficially, approximately between 0.3 μm and5 μm. Here the thickness d is 2.5 μm.

FIG. 3 is a cross-sectional view illustrating a line of fracture createdin an organic EL display device according to a reference. FIG. 4 is across-sectional view illustrating a line of fracture created in theorganic EL display device 1 according to the first embodiment. Therelationship (d/h)≥2 applies to the organic EL display deviceillustrated in FIG. 3. In the organic EL display device 1 of thisembodiment, the relationship (d/h)<2 holds.

The buffer layer 33 lower in hardness than the barrier layer 31A and thebarrier layer 31B in order to reduce stress. Hence, the buffer layer 33is susceptible to fracture caused by stress—sheer stress—imposed fromthe barrier layer 31B placed above the buffer layer 33 and createdbecause of temperature change, Here, portions, of the buffer layer 33,having contact with the barrier layer 31A and the barrier layer 31B areclosely attached to the barrier layer 31A and the barrier layer 31B.Thus, an intermediate portion of the buffer layer 33 in a verticaldirection is most vulnerable against the shear stress.

Hence, as shown in FIG. 3, the organic EL display device according tothe reference has a line of fracture 35 continuously developed near themiddle of the buffer layer 33, making a multilayer sealing film 102 moreprone to delamination.

In contrast, as shown in FIG. 4, the relationship (d/h)<2 holds in theorganic EL display device 1 of this embodiment. That is why the line offracture 35 develops only in a region between the edge covers 18, anddoes not develop continuously. Hence, even if the line of fracture 35develops in the buffer layer 33, the delamination of the multi layersealing film 2 may be effectively reduced.

Described next is an exemplary method of manufacturing the organic ELdisplay device 1 of this embodiment. FIGS. 5 to 8 are cross-sectionalviews illustrating a method of manufacturing the organic EL displaydevice 1 according to this embodiment.

First, in a step shown in FIG. 5, the TFTs 11 for driving the organic ELelements 4 are formed at predetermined intervals on the elementsubstrate 10. The element substrate 10 may be a glass substrate having asize of 320 mm×400 mm and a thickness of 0.7 mm. Materials for the TFTs11 may include amorphous silicon, polysilicon, indium gallium zinc oxide(InGaZnO), indium gallium tin oxide (InGaSnO), and indium tin zinc oxide(InSnZnO). The TFTs 11 are manufactured by a known technique.

Next, in a step shown in FIG. 6, photosensitive acrylic resin is appliedby spin coating on the element substrate 10 on which the TFTs 11 areformed. The photosensitive acrylic resin is exposed to a predeterminedamount (e.g., 360 mJ/cm²) of light through an exposure mask with apredetermined exposure pattern. Then, the photosensitive acrylic resinis developed, using an alkaline developer. As a result, the interlayerinsulating film 21 having a thickness of, for example, 2 μm is formed.After the exposure, the interlayer insulating film 21 is baked inpost-baking under a predetermined condition (e.g., at a temperature of220° C. for 120 minutes).

At this time, on the interlayer insulating film 21, the contact holes 23(shaving a diameter of 5 μm, for example) are formed for electricallyconnecting the first electrodes 13 to the TFTs 11.

In a step shown in FIG. 7, an ITO film is formed by sputtering, exposedto light and developed by photolithography, and patterned by etching toform the first electrodes 13 on the interlayer insulating film 21. Atthis time, the first electrodes 13 have a thickness of approximately 100nm, for example. After the exposure, the first electrodes 1 are baked inpost-baking under a predetermined condition (e.g., at a temperature of220° C. for 120 minutes). The first electrodes 13 are electricallyconnected to the TFTs 11 via the contact holes 23 formed in theinterlayer insulating film 21.

Next, photosensitive acrylic raisin is used to form the edge covers tocover the entire peripheral edges of the first electrodes 13, using asimilar method employed when the interlayer insulating film 21 isformed. At this time, the edge covers 18 have a thickness ofapproximately 2 μm, for example.

Then, the organic EL layer 17 including the light-emitting layer isformed above the first electrodes 13, and after that, the secondelectrode 14 is formed above the organic EL layer 17. The organic ELlayer 17 and the second electrode 14 are formed by vapor deposition,using a metal mask.

More specifically, first, the element substrate 10 having the firstelectrodes 13 is placed in a chamber of a vapor deposition system. Thechamber interior of the vapor deposition system is kept at a vacuumdegree of 1×10⁻⁵ Pa to 1×10⁻⁴ Pa by a vacuum pump. Moreover, the elementsubstrate 10 having the first electrodes 13 is placed while two sides ofthe element substrate 10 is secured with a pair of substrate holdersprovided to the interior of the chamber.

In a evaporation source, source materials (evaporants) for the holeinjection layer, the hole transport layer, the light-emitting layer, theelectron transport layer, and the electron injection layer aresequentially evaporated and then stacked to form the organic EL layer 17in pixel regions.

Then, the second electrode 14 is formed above the organic EL layer 17.As a result, the organic EL element 4 including the first electrodes 13,the organic EL layer 17, the second electrode 14, and the edge covers 18are formed above the element substrate 10.

Note, in the above configuration, the organic EL element 4 includes thefirst electrodes 13 as anodes and the second electrode 14 as a cathode.In contrast, the organic EL element 4 may include the first electrodes13 as cathodes and the second electrode 14 as an anode. In this case,the materials for both of the electrodes are switched, and the layers inthe organic EL layer 17 are stacked in the reverse order.

Furthermore, in the above configuration, the organic EL element 4includes the first electrodes 13 as transparent electrodes and thesecond electrode 14 as a reflective electrode. In this configuration,the organic EL display device 1 is a bottom-emitting element which emitslight toward the element substrate 10 when observed from the organic ELelement 4. In contrast, the first electrodes 13 may act as reflectiveelectrodes and the second electrode 14 may act as a transparentelectrode or a translucent electrode. In this case, the organic ELelement 4 is a top-emitting element which emits light toward oppositeside of the element substrate 10 when observed from the organic ELelement 4.

Note, for example, that a crucible containing the evaporants is used asthe evaporation source. The crucible is placed in a lower position in achamber, and includes a heater, which heats the crucible.

The heat of the heater allows the temperature inside the crucible toreach the evaporation temperatures of the evaporants so that theevaporants contained in the crucible become evaporated molecules andrise upward and goes out of the chamber.

A specific example formation of the organic EL layer 17 and the secondelectrode 14 is as follows. First, the hole injection layer is formed,in common among all the RGB pixels, above the first electrodes 13patterned on the element substrate 10. Containingm-MTDATA(4,4′,4″-tris[phenyl(m-tolyl)amino]triphenylamine), the holeinjection layer is formed via a mask with a thickness of, for example,25 nm.

Then, the hole transport layer is formed, in common among all the RGBpixels, above the hole injection layer. Containingα-NPD(4,4′-bis[phenyl(1-naphtyl)amino]biphenyl), the hole transportlayer is formed via a mask with a thickness of, for example, 30 nm.

Next, the light-emitting layer of red color is formed above the holetransport layer provided in the red pixel regions. Containing a mixtureof 30 wt % of 2, -6bis(4′-methoxyphenyl)amino)styryl)-1,5-dicyanonaphthalene (BSN) with di(2-naphthyl)anthracene (ADN), thelight-emitting layer of red color is formed via a mask with a thicknessof, for example, 30 nm.

After that, the light-emitting layer of green color is formed above thehole transport layer provided in the green pixel regions. Containing amixture of 5 wt % of coumarin 6 with ADN, the light-emitting layer ofgreen color is formed via a mask with a thickness of, for example, 30nm.

Then, the light-emitting layer of blue color is formed above the holetransport layer provided in the blue pixel regions. Containing a mixtureof 2.5 wt % of 4,4′bis(2-[4-(N,N-diphenylamino)phenyl]vinyl)biphenyl(DPAVBi) with ADN, the light-emitting layer in blue color is formed viaa mask with a thickness of, for example, 30 nm.

Next, the electron transport layer is formed, in common among all theRGB pixels, above the light-emitting layer of all the colors. Containing8-hydroxyquinoline aluminum (Alq3), the electron transport layer isformed via a mask with a thickness of, for example, 20 nm.

After that, the electron injection layer is formed above electrontransport layer. Containing lithium fluoride (LiF), the electroninjection layer is formed via a mask with a thickness of, for forexample, 0.3 nm. Then, the second electrode 14 containing aluminum (Al)is formed with a thickness of, for example, 10 nm by vacuum vapordeposition.

After that, in a step shown in FIG. 8, the sealing film 2 is formedabove the element substrate 10 to cover the organic EL element 4.

Specifically, in the step, such inorganic materials as silicon nitride(SiNx), silicon dioxide (SiO₂), and aluminum oxide (Al₂O₃) are depositedon surfaces of the element substrate 10 and the organic EL element 4 byplasma CVD, atomic layer deposition (ALD), and sputtering to form thebarrier layer 31A with a thickness of approximately 0.3 μm. Next, suchorganic materials as acrylate, polyurea, parylene polyimide, andpolyamide are deposited on the surfaces of the element substrate 10 andthe organic EL element 4 by plasma polymerization and vacuum vapordeposition or other methods to form the buffer layer 33 having athickness of approximately 2.5 μm. Then, such inorganic materials assilicon nitride (SiNx), silicon dioxide (SiO₂), and aluminum oxide(Al₂O₃) are deposited on the surfaces of the element substrate 10 andthe organic EL element 4 by plasma CVD, ALD, and sputtering to form thebarrier layer 31B having a thickness of approximately 0.3 μm.

Note that the multilayer sealing film 2 may include at least one barrierlayer and at least one buffer layer. Multiple barrier layers and bufferlayers may alternately be provided.

(Second Embodiment)

FIG. 9 is a cross-sectional view illustrating a structure of amultilayer sealing film in an organic EL display device according to asecond embodiment.

The organic EL display device of this embodiment is the same inconfiguration as the organic EL display device 1 according to the firstembodiment except for a configuration of the multilayer sealing film 2.Described below is the configuration of the multilayer sealing film 2.

As shown in FIG. 9, the organic EL display device in this embodimentincludes the multilayer sealing film 2 having the barrier layer 31A andthe barrier layer 31B and a barrier layer 31C, and a buffer layer 33Aand a barrier layer 33B. The barrier layers and the buffer layers arealternately stacked. Moreover, a relationship (d1/h1)<2 holds where h1is a height of a protrusion directly below the buffer layer 33A and d1is a thickness of the buffer layer 33A. Furthermore, a relationship(d2/h2)<2 holds where h2 is a height of a protrusion directly below thebuffer layer 33B and d2 is a thickness of the buffer layer 33B.

The height h1 of the protrusion directly below the buffer layer 33Aranges approximately between 0.5 μm and 3 μm, for example. Here theheight h1 is 1.6 μm. The thickness d1 of the buffer layer 33Aapproximately ranges between 0.3 μm and 5 μm. Here the thickness d1 is2.5 μm. The height h2 of the protrusion directly below the buffer layer33B ranges approximately between 0.2 μm and 1.5 μm, for example. Herethe h2 is 0.8 μm. The thickness d2 of the buffer layer 33B approximatelyranges between 0.3 μm and 5 μm. Here the thickness d2 is 1.2 μm.

Thus, when the multilayer sealing film 2 includes (i) n buffer layers(where n is an integer larger than or equal to 2) or iii) n barrierlayers or (n+1I) barrier layers, a relationship (d_(n)/h_(n))<2 holdswhere d_(n) is a thickness of an n-th buffer layer, from the bottom,among the n buffer layers and h_(n) is a height of a protrusion directlybelow the n-th buffer layer. Note that in the above first embodiment,the relationship n=1 holds. In this case, the relationship(d_(n)/h_(n))<2 also holds (where d1=d, and h1=h).

According to this structure, even though multiple buffer layers areprovided, a continuous line of fracture does not develop in each bufferlayer. Such a structure may effectively keep a film from delamination.

A thicker barrier layer causes a greater stress imposed on theunderlayer, inducing delamination on an interface between the barrierlayer and the buffer layer. Hence, a barrier layer may have a thicknesssmaller than or equal to a certain thickness. The organic EL displaydevice of this embodiment includes multiple barrier layers. Thus, evenif each barrier layer is made thin, the barrier layers may keep anorganic EL element from moisture and oxygen more effectively.

Furthermore, in the example shown in FIG. 9, the barrier layer 31A is abottom-most layer of the multilayer sealing film 2. In this case, heightof a protrusion directly below each buffer layer is almost equal to aheight of a protrusion of the organic EL element 4. More accurately, theheight h of the protrusion directly below the n-th buffer layer from thebottom is equal to a difference in level between (i) a top thee of aportion, of the n-th barrier layer from the bottom, forming theprotrusion and (ii) an other top face of a portion, of the n-th barrierlayer from the bottom, formed between protrusions including theprotrusion.

Note that as shown in FIG. 10, the buffer layer 33A may be thebottom-most layer of the multilayer sealing film 2. In either case,alternately formed barrier layers and buffer layers may allow the bufferlayers to reduce stress imposed from the barrier layers.

Moreover, when the buffer layer 33A is the bottom-most layer of themultilayer sealing film 2, the buffer layer 33A may effectively reducethe stress caused by the barrier layer 31B above the buffer layer 33A.Such a structure may keep a film from delamination. Furthermore, thebuffer layer 33A may be provided directly above the organic EL element4. Such a structure may keep the organic EL element 4 from a damage tobe caused by a plasma treatment and a UV treatment employed when thebarrier layer 31B is formed.

(Third Embodiment)

FIG. 11 is a cross-sectional view illustrating an organic EL displaydevice according to a third embodiment. FIG. 12 is an enlargedcross-sectional view illustrating the organic EL display deviceaccording to the third embodiment.

The organic EL display device of this embodiment includes: a sealingsubstrate 41 facing the element substrate 10 and acting as a secondsubstrate; and a sealing material 43 interposed between the elementsubstrate 10 and the sealing substrate 41 and boding the elementsubstrate 10 and the sealing substrate 41 together to seal the organicEL element 4. Moreover, the organic EL display device of this embodimentincludes: a filler 37 filled in a gap between the organic EL element 4and the sealing substrate 41; and a color filter 39 provided to aundersurface of the sealing substrate 41. The filler 37 may function asa getter (i.e., a function to adsorb oxygen and moisture). Furthermore,the organic EL element 4 is a top-emitting element, and emits lighttoward the sealing substrate 41 via the color filter 39. Except for theabove configurations, the organic EL display device of this embodimentis the same in configuration as the organic EL display device 1according to the first embodiment.

Hence, as illustrated in FIG. 12, the relationship (d/h)<2 holds where dis a thickness of the buffer layer 33 and h is a height of a protrusioncovered with the buffer layer 33. The height h of the protrusion rangesapproximately between 0.5 μm and 3 μm, for example. Here, the height his 1.6 μm. The thickness d of the buffer layer 33 ranges approximatelybetween 0.3 μm and 5 μm as described above. Here, the thickness is 2.5μm.

Such a structure allows a line of fracture to be less likely to developin the buffer layer 33, effectively reducing delamination of themultilayer sealing film 2.

A material for filler 37 includes a curable ma such as an epoxy resin ora non-curable material such as a silicon resin. In view of improvingadsorption of moisture, the filler 37 contains an alkaline earth metaloxide such as calcium oxide (CaO) and barium oxide (BaO) and a desiccantsuch as silica gel and zeolite.

The sealing material 43 to bond the element substrate 10 and the sealingsubstrate 41 together is for securing the element substrate 10 andsealing substrate 41. Materials for the sealing material 43 may includesuch ultraviolet (UV) curable resins as an epoxy resin and an acrylicresin, and such moisture-permeable materials as a thermosetting resin.Note that the sealing mate 43 may be omitted when a curable filler isused and the curable filler and the multilayer sealing film 2 reliablykeep the organic EL display element 4 from moisture and oxygen.

As shown FIG. 11, in the organic EL display device 1, a frame region(i.e., a seal formation region) 16 in which the sealing material 43 isplaced is defined around the display region 15. As shown in FIG. 11 thesealing material 43 is provided in the frame region 16 and shaped into aframe above the multilayer sealing film 2 to seal the organic EL element4, and bonds the element substrate 10 and the sealing substrate 41together.

The color filter 39 functions to modulate light emitted from the organicEL element 4. For example, when the organic EL element 4 emits whitelight, the color filter 39 having an RGB pattern modulates the whitelight coming from each pixel region into the colors R, G, and B.

When the pixel regions emit respective R, G, and B light rays, the whitelight passes through a color pattern, of the color filter 39,corresponding to one of the light rays. Such a feature may improve colorpurity of each color and reduce shift of tinge observed when a viewingangle changes. When the color filter 39 is provided, the color filter 39and the element substrate 10 may be positioned for each pixel, and thenthe element substrate 10 and the sealing substrate 41 with which thecolor filter 39 is previously provided may be bonded together.

Note that the color filter 39 may be omitted when a single color isacceptable for the emitted light and the color purity and the shift oftinge are nothing to do with the emitted light.

Moreover, employing substrates which bend or curve as the elementsubstrate 10 and the sealing substrate 41 makes it possible to produce aflexible display and a bendable display.

Note that a gap spacer (not shown) may be provided above the elementsubstrate 10 to reduce the risk that the sealing substrate 41 hits theelement substrate 10, damaging the organic EL element 4.

The organic EL display device of this embodiment may effectively keepthe organic EL element 4 from external moisture and oxygen, contributingto reliably reducing deterioration of the organic EL element 4.

Next, such a material as the above epoxy resin is applied onto thesealing substrate 41, using dispending, mask printing, screen printing,or other methods to form the sealing material 43 into a frame shape.Here, an example of the sealing substrate 41 is a glass substrate havinga substrate size of 320 mm×400 mm, and a thickness of 0.7 mm.

Note that the seating material 43 may include a spacer (not shown) toregulate a gap between the element substrate 10 and the sealingsubstrate 41. This spacer contains for example, silicon dioxide (SiO₂).

Moreover, in this embodiment, an epoxy resin is beneficially used as amaterial for the sealing material 43, and a viscosity of the materialranges between 100 Pa·s and 1000 Pa·s. However, the viscosity shall notbe limited to this range as long as the material can be patterned by,for example, lithographing with dispending or screen printing asdescribed above.

Furthermore, when an epoxy resin is used as a material for the sealingmaterial 43, the epoxy resin may act as a desiccant. When the sealingmaterial 43 is cured, a material for the sealing material 43beneficially produces no (or little) outgas. In view of reducing damageto the light-emitting layer, the material for the sealing material 43 isbeneficially low in shrinkage when the sealing material 43 is cured.

When a thermosetting material is used for the sealing material 43, thethermosetting material may beneficially be curable at or below 100° C.,taking thermal influence on the light-emitting layer into consideration.Beneficially, the sealing material 43 is low in moisture permeation.

After that, the material for the filler 37 is applied, apart from thesealing material 43, inside, the sealing material 43 on the sealingsubstrate 41 by dispending, mask printing, drop injection, or othermethods. In place of an applicable material, a sheet-like material mayalso be used.

Next, in a vacuum atmosphere, the sealing substrate 41 provided with thesealing material 43 is stacked above the element substrate 10 providedwith the organic EL element 4 so that the material overlaps the organicEL element 4. A surface of the sealing material 43 on the sealingsubstrate 41 is placed on a surface of the multilayer sealing film 2 inthe frame region 16.

Then, under a predetermined condition (e.g., under a pressure of 100 Paor lower), the interior of the sealing material 43 is kept in airtightvacuum. In the vacuum atmosphere, the sealing substrate 41 is movedtoward the element substrate 10 and pressurized with the sealingmaterial 43 sandwiched between the sealing film 2 and the sealingsubstrate 41. As a result, the element substrate 10 and the sealingsubstrate 41 are bonded together via the sealing material 43.

Next, after purging the vacuum state to the atmospheric pressure (i.e.,bringing the vacuum state back to an atmospheric pressure state), thesealing, substrate 41 is irradiated with ultraviolet (UV) light so thatthe resin forming the sealing material 43 cures. As a result, theorganic EL display device shown in FIG. 11 is manufactured.

The above organic EL display devices are examples of the embodiments ofthe present disclosure. Such factors as a size, a shape, and amanufacturing, condition of each member may receive any givenmodification unless otherwise departing from the scope of the presentdisclosure.

For example, in the above embodiments, the organic EL display device 1has been described as an example of a display device. Instead, thepresent disclosure may be applicable to other display devices such as aliquid crystal display.

[Example]

Inventors of this application made the organic EL display device 1illustrated in FIGS. 1 and 2, and studied whether the multilayer sealingfilm 2 would delaminate. An organic silicon polymer was used as amaterial for the buffer layer 33. Silicon nitride was used as amaterial, for the barrier layer 31A and the barrier layer 31Brespectively placed below and above the buffer layer 33. The barrierlayer 31A and the barrier layer 31B each had a thickness of 0.5 μm. Thebuffer layer 33 had a Vickers hardness of 26.

The stacked sealing films 2 were formed so that pairs of the thickness dof the buffer layer 33 and the height h of the protrusion from anunderlayer (d, h) were determined as follows: (0.43 μm, 1.5 μm), (0.48μm, 0.7 μm), (2.5 μm, 1.6 μm), (2.7 μm, 1.4 μm), (2.8 μm, 1.2 μm), and(2.3 μm, 0.8 μm). Then, the multilayer sealing film 2 was checked fordelamination. Specifically, adhesive cellophane tape (manufactured by,for example, Nichiban Co., Ltd.) was attached to the multi layer sealingfilm 2. Then, the attached tape was stripped off with a hand at a speedof approximately 100 cm/s. Here, the inventors observed visually andmicroscopically whether the multilayer sealing film 2 had separated fromthe underlayer and had been attached to the stripped tape. Table 1 showsthe results.

TABLE 1 Thickness of Height of Protrusion Buffer Layer from anUnderlayer Film d (μm) h (μm) d/h Separation 0.43 1.5 0.3 No 0.48 0.70.7 No 2.5 1.6 1.6 No 2.7 1.4 1.9 No 2.8 1.2 2.3 Yes 2.3 0.8 2.9 Yes

The results in Table 1 show that the inventors observed no filmdelamination when the value d/h was smaller than at least 2.0, and filmdelamination when the value d/h was 2.0 or greater.

Moreover, the inventors of this application checked whether themultilayer sealing film 2 would laminate when a material contained inthe buffer layer 33 was changed so that the hardness of the buffer layer33 changed. The buffer layer 33 had a thickness of 2 μm, and the barrierlayer 31A and the barrier layer 31B each had a thickness of 0.5 μm.

A Vickers hardness of the buffer layer 33 was measured by a method whichcomplies with ISO14577. Specifically, the inventors measured the Vickershardness with a microhardness tester (e.g., H100C manufactured byFischer Instruments K.K.), using a specimen formed on glass to have athickness ranging between 0.5 μm and 2 μm. Table 2 shows the results ofthe measurement.

TABLE 2 Vickers Hardness Film Separation 80 No 68 No 58 No 49 No 42 No35 YesThe results in Table 2 show that, on a planarized surface, no filmseparation was observed when the Vickers hardness was 42 or higher, andfilm delamination was observed when the Vickers hardness was as low as35. In contrast, when the value d/h was smaller than 2.0, the inventorsobserved no film delamination even though the Vickers hardness wasdecreased to as low as 26.

The buffer layer 33 having a lower hardness is likely to reduce moreeffectively a stress imposed from the barrier layer 31B. Since theorganic EL display device 1 of this embodiment reduces the risk of filmdelamination, the buffer layer 33 to be used may be lower in hardnessthan a typical buffer layer, contributing to reducing the risk of filmdelamination while maintaining barrier performance of the multilayersealing film 2.

INDUSTRIAL APPLICABILITY

As can be seen, the organic EL display devices according to examples ofthe present disclosure may be applicable to such various appliancesequipped with display devices as TVs and cellular phones.

DESCRIPTION OF REFERENCE CHARACTERS

-   1 Organic EL Display-   2 Stacked Sealing Film-   4 Organic EL Element-   10 Element Substrate-   11 TFT-   13 First Electrode-   14 Second Electrode-   15 Display Region-   15B, 15G, 15R Pixel Region-   16 Frame Region-   17 Organic EL Layer-   18 Edge Cove-   21 Interlayer Insulating Film-   23 Contact Hole-   31A, 31B, 31C Barrier Layer-   33, 33A, 33B Buffer Layer-   35 Line of Fracture-   37 Filler-   39 Color Filter-   41 Sealing Substrate-   43 Sealing Material

The invention claimed is:
 1. An organic EL display device comprising: afirst substrate; an organic EL element provided above the firstsubstrate; and multilayer sealing film provided above the firstsubstrate to cover the organic EL element, the multilayer sealing filmincluding a first barrier layer, a buffer layer having a lower hardnessthan the first barrier layer, and a second barrier layer covering thebuffer layer, wherein the organic EL element covered with the multilayersealing film includes: first electrodes (13) arranged above the firstsubstrate (10); an organic EL layer (17) formed above the firstelectrodes (13); a second electrode (14) formed above the organic ELlayer (17); and an edge cover (18) provided to cover peripheral edges ofthe first electrodes (13) and open a portion of the first electrodes(13), in a display region, the organic EL element includes at least oneprotrusion formed with the edge cover (18), wherein (d/h)<2 and h<d,where h is a difference between a bottom face of the buffer layer abovethe at least one protrusion and a bottom face of the buffer layer abovethe first electrode having an opening formed with the edge cover, and dis a difference between a bottom face of the buffer layer above thefirst electrode having the opening formed with the edge cover and a topfine of the buffer layer above the first electrode having the openingformed with the edge cover.
 2. The organic EL display device of claim 1,wherein the multilayer sealing film includes n buffer layers, the nbuffer layers including the buffer layer, where n is an integer greaterthan or equal to 2, an n-th buffer layer having at least one protrusionon a bottom surface thereof, and wherein (d_(n)/h_(n))<2, where d_(n) isa thickness of the n-th buffer layer, from a bottom of the sealing film,among the a buffer layers and h_(n) is a height of the at least oneprotrusion on the bottom surface of the n-th buffer layer.
 3. Theorganic EL display device of claim 1, wherein the barrier layer includesn barrier layers or (n+1) barrier layers, and the barrier layer and thebuffer layer are alternately provided.
 4. The organic EL display deviceof claim 1, wherein the barrier layer is a bottom-most layer of themultilayer sealing film.
 5. The organic EL display device of claim 1,wherein the height h of the protrusion on the bottom surface of the n-thbuffer layer from the bottom is equal to a difference in level between(i) a top face of a portion, of the n-th barrier layer from the bottom,forming the protrusion and (ii) an other top face of a portion, of then-th barrier layer from the bottom, formed between protrusions includingthe protrusion.
 6. The organic EL display device of claim 1, furthercomprising: a second substrate provided above the first substrate andthe organic EL element; and a filler filled between the multilayersealing film and the second substrate.
 7. The organic EL display deviceof claim 1, wherein the barrier layer is a top-most layer of themultilayer sealing film.
 8. The organic EL display device of claim 1,wherein the first barrier layer and the second barrier layer contain aninorganic material.
 9. The organic EL display device of claim 1, whereinthe buffer layer contains an organic material.
 10. The organic ELdisplay device of claim 1, wherein the organic EL display device is aflexible display.
 11. The organic EL display device of claim 1, whereinthe organic EL element contains polysiloxane, silicon oxycarbide,acrylate, polyurea, parylene, polyimide, or polyamide.
 12. The organicEL display device of claim 1, further comprising: first electrodesarranged in a matrix; and edge covers provided to cover peripheral edgesof the first electrodes and regions in which the first electrodes arenot provided, wherein each of the edge covers forms the protrusion andthe other protrusion.
 13. The organic EL display device of claim 1,wherein the edge covers cover all the peripheral edges of the firstelectrodes.
 14. The organic EL display device of claim 1, wherein themultilayer sealing film further includes n buffer layers, wherein n isan integer greater than or equal to 2, the n buffer layers includes thebuffer layer, wherein an n-th buffer layer having at least oneprotrusion on a bottom surface of the n-th buffer layer, the at leastone protrusion on the bottom of the n-th buffer layer overlaps with oneprotrusion of each of the other buffer layers in a directionperpendicular to the first substrate.
 15. The organic EL display deviceof claim 1, wherein (d1/h1)<2 and h1<d1, where h1 is a height of the atleast one protrusion on the bottom surface of the buffer layer and d isa thickness of the buffer layer between the at least one protrusion andanother protrusion on the bottom surface of the buffer layer adjacent tothe at least one protrusion.
 16. The organic EL display device of claim1, wherein (d_(n)/h_(n))<2 and h_(n)<d_(n), where d_(n) is a thicknessof the n-th buffer layer, and h_(n) is a height of the at least oneprotrusion on the bottom surface of the n-th buffer layer.
 17. Theorganic EL display device of claim 1, wherein h1>h_(n) and d1>d_(n). 18.The organic EL display device of claim 1, wherein the height h rangesfrom 0.5 μm to 3 μm.
 19. The organic EL display device of claim 1,wherein the thickness d ranges from 0.3 μm to 100 μm.